Fluid abrasive machining method and apparatus thereof

ABSTRACT

In a fluid abrasive machining method for abrasively machining a fine pore on a work ( 5 ) to be machined by supplying a slurry ( 7 ) which is an abrasive machining fluid from a supplying device ( 2 ) to the work to be machined comprising steps of: supplying the slurry to the work to be machined from the supplying device; measuring a first pressure (P 1 ) upstream in a discharge side of the supplying device; measuring a second pressure (P 2 ) downstream of a measuring point of the first pressure (P 1 ) and at an upstream side of the work to be machined; calculating a pressure difference (dp) between the first pressure and the second pressure; and terminating a machining operation when the pressure difference dp reaches a specific value. A fluid abrasive machining apparatus ( 100 ) which can perform the above-mentioned fluid abrasive machining method is provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fluid abrasive machining method and to a fluid abrasive machining apparatus for effecting the method and, more particularly, to a machining method, and to a machining apparatus with high precision, for drilling a fine pore using an abrasive slurry.

2. Description of the Related Art

Many apparatuses having a fine pore formed with high precision, for example, a tip of a fuel injection nozzle, an injection hole of a caburetor, an orifice for regulating a flow rate of fluid, an injection nozzle of a printer, etc. are known. Laser machining, electro-beam machining, electrical discharge machining and the like are known as machining methods for drilling a fine pore. However, in case where the above-mentioned methods cannot drill a fine pore with a sufficient precision, a fluid abrasive machining method may be employed. As an example, a fluid abrasive machining method is used for drilling a fine pore of an orifice of a diesel common rail type fuel injector which is applied to a diesel engine. Recently, a diesel engine tends to have common rail type fuel injectors and a diesel engine having common rail type fuel injectors is installed on a vehicle in the range from a small automobile with approximately 80 KW output power to a large truck. If the output flow rate of the fuel injector includes some errors, the fuel consumption efficiency of a diesel engine is decreased, so that an economic performance thereof is deteriorated and, as a result, polluting contaminates in the exhaust gas are increased and the environment may be deteriorated.

The flow rate error of a diesel common rail type injector is greatly influenced by a static oil flow rate precision of an orifice which is a component of the injector so that the orifice is finished by the fluid abrasive machining method in order to adjust the size of the orifice. In the fluid abrasive machining method, a slurry, which is produced as a mixture of grinding particles and oil and is discharged from a cylinder by a movement of a piston, flows through the orifice, so that the diameter of an orifice hole is enlarged and the inlet periphery of the orifice hole is rounded.

In the fluid abrasive machining of a fine pore (or micro-pore), a measuring method in which the diameter of the fine pore is measured by measuring the flow rate of a specific fluid, when the specific fluid flows through the fine pore at a constant pressure, may be used. Some products such as a fuel injection nozzle, which have a function to pass a fluid at a specific flow rate, have a product performance which is determined by a machining precision. The product performance of such a product can be directly judged from a target machining precision value thereof which can be examined by measuring a flow rate of fluid flowing though the product. In the fluid abrasive machining, the finishing state of a product can be judged and whether the product has a specified performance due to the machining can be confirmed by measuring the flow rate of the abrasive fluid so that such a measuring method may be performed.

For example, in a fuel injection nozzle for a vehicle, etc., an injection hole for injecting fuel has been required to have an extremely high accuracy in order to attain a flow rate performance standard thereof and, therefore, conventionally it was common that the flow rate of a slurry which was an abrasive material or a displacement (movement distance) of a piston corresponding to the flow rate of the slurry was monitored and just when the flow rate of the slurry reached a specified flow rate value or the displacement (movement distance) of the piston reached a specified alternate value corresponding to the specified flow rate of the slurry, the machining operation was terminated (refer to, for example, Patent document 1 or 2). According to the conventional method, however, an expensive flow meter or an expensive monitoring device was required so that there was a problem in which the cost of facilities increases.

Another technique of the fluid abrasive machining method has been proposed but it does not disclose the present invention (refer to, for example, Patent document 3).

[Patent document 1] Unexamined Published Japanese Translation of PCT International Publication No. 11-510437

[Patent document 2] Japanese Examined Patent Publication (Kokoku) No. 7-85866

[Patent document 3] Japanese Unexamined Patent Publication (Kokai) No. 2004-284014

SUMMARY OF THE INVENTION

The above-described circumstances being taken into account, the present invention has been developed and an object of the present invention is to provide a fluid abrasive machining method capable of controlling a fluid abrasive machining without using an expensive flow meter, and an apparatus for performing the method.

In a first aspect of the present invention, in order to attain the above-described object, a fluid abrasive machining method for abrasively machining a fine pore on a work (5) to be machined by supplying a slurry (7), which is an abrasive machining fluid, from a supplying device (2) to the work to be machined comprises steps of: supplying the slurry to the work to be machined from the supplying device; measuring a first pressure (P1) at an upstream discharge side of the supplying device; measuring a second pressure (P2) at a downstream of a measuring point of the first pressure (P1) and at an upstream side of the work to be machined; calculating a pressure difference (dp) between the first pressure and the second pressure; terminating a machining operation when the pressure difference dp reaches a specific pressure difference value.

By configuring as described above, it is possible to machine a fine pore with a high precision on a work to be machined by a fluid abrasive machining method, without using an expensive flow meter.

In a second aspect of the present invention according to the above-mentioned first aspect, control is performed so that the first pressure (P1) is always maintained at a substantially constant pressure during a fluid abrasive machining operation.

According to the present aspect, it is possible to machine a fine pore, which has a high precision and has a specific flow rate performance, on a work by a way in which the first pressure (P1) is controlled to be always maintained at a substantially constant pressure, the second pressure (P2) is monitored and when the second pressure (P2) reaches a specific pressure value, the operation of a machining is terminated.

In a third aspect of the present invention according to the above-mentioned first aspect, a control is performed so that the second pressure (P2) is always maintained at a substantially constant pressure in a fluid abrasive machining operation.

According to the present aspect, it is possible to machine a fine pore, which has a high precision and has a specific flow rate performance, on a work by a way in which the second pressure (P2) is controlled to be always maintained at a substantially constant pressure, the first pressure (P1) is monitored and when the first pressure (P1) reaches a specific pressure value, the operation of a machining is terminated.

In a fourth aspect of the present invention according to any one of the above-mentioned first to third aspects, the object to be machined is a fine pore of a fuel injector for a diesel engine.

According to the present aspect, an application for a fluid abrasive machining method of the present invention is concretely described.

In a fifth aspect of the present invention, a fluid abrasive machining apparatus (100) for abrasively machining a fine pore on a work (5) to be machined by supplying a slurry (7), which is an abrasive machining fluid, to the work to be machined comprises: a supplying device (2) for supplying the slurry (7); a measuring means for measuring a pressure difference (dp) between a first pressure (P1) at an upstream in a discharge side of the supplying device and a second pressure (P2) at a downstream of a measuring point of the first pressure (P1) and at an upstream side of the work to be machined; and a terminating means for terminating a machining operation when the pressure difference (dp) reaches a specific pressure difference value.

By configuring as described above, it is possible to machine a work to form a fine pore having high precision thereon by a fluid abrasive machining method, without using an expensive flow meter.

In a sixth aspect of the present invention according to the above-mentioned fifth aspect, the fluid abrasive machining apparatus further comprises: a first pressure sensor (14) for measuring the first pressure (P1); and a second pressure sensor (15) for measuring the second pressure (P2).

According to the present aspect, a measuring means for measuring the pressure difference (dp) is concretely described.

In a seventh aspect of the present invention according to the above-mentioned fifth or sixth aspect, the work (5) to be machined is a fuel injector for a diesel engine.

According to the present aspect, an application for a fluid abrasive machining apparatus of the present invention is concretely described.

In the above-mentioned explanation of the present invention, symbols or numbers in the parentheses ( ) are attached in order to show correspondence to the embodiments shown below.

The present invention may be more fully understood from the description of the preferred embodiments of the invention set forth below, together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a diagrammatic illustration showing a configuration of an embodiment of a fluid abrasive machining apparatus according to the present invention.

FIG. 2 is a graph showing a relationship between a flow rate of a slurry and a piping line pressure loss in a fluid abrasive machining method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of a fluid abrasive machining method and a fluid abrasive machining apparatus according to the present invention are described below, and in detail, based on the drawings.

First, the principle of the present invention is explained.

As shown in FIG. 2, it has been confirmed by an experiment that a flow rate of fluid flowing through a product (the product is a fuel injection nozzle of a diesel engine in this embodiment) is proportional to the pressure loss dP between an upstream side (for example, a supply side of a slurry (abrasive fluid)) and a downstream side (for example, just in front of the product) of a piping line of the fluid abrasive machining apparatus. This phenomenon appears in a case in which when the diameter of a piping line is constant, the flow rate of fluid flowing through the product to be examined is proportional to a mean flow velocity of the fluid at an upstream side and on the other hand, in a case of a laminar flow, the mean flow velocity of the fluid at the upstream side is proportional to the pressure loss dP between the upstream side and the downstream side of the piping line of the fluid abrasive machining apparatus. This phenomenon is expressed by a hargen poiseuille equation as shown below. dPf=32*μ*L*u/D ²   [equation 1]

Where dPf is a pressure loss, D is an inner diameter of a piping line, L is a length, μ is a viscosity coefficient of a slurry, and u is a mean velocity of the slurry in a piping line.

In other words, in a fluid abrasive machining apparatus, this equation suggests that the flow rate performance of the product (the flow rate of a slurry flowing through the product at a specific pressure) can be controlled by monitoring the pressure loss in an arbitrary piping line through which the slurry flows, during an abrasive machining operation.

FIG. 1 diagrammatically shows a structure of a first embodiment of a fluid abrasive machining apparatus according to the present invention. The fluid abrasive machining apparatus 100 according to the first embodiment comprises: a slurry tank 1 for storing a slurry 7 which functions as abrasive fluid and comprises a mixer 4; a slurry supplying device 2 for sucking the slurry 7 from the slurry tank 1 to supply it to a work 5 to be machined; and a control section 20 for controlling the fluid abrasive machining apparatus 100. In this embodiment, the work 5 to be machined is a fuel injection nozzle for an engine. The slurry supplying device 2 is a cylinder 2 which comprises a piston 6 which reciprocates in the cylinder 2 and the slurry 7 is sucked and pumped by a reciprocating motion of the piston 6. The fluid abrasive machining apparatus 100 further comprises three control valves. A first control valve 11 is arranged on the upstream of the cylinder 2, a second control valve 12 is arranged on the downstream of the cylinder 2 and a third control valve 13 is arranged on the upstream of the nozzle 5, respectively, as shown in FIG. 1. The fluid abrasive machining apparatus 100 further comprises a first pressure sensor 14 arranged near and on the downstream of the second control valve 12 and a second pressure sensor 15 arranged near and on the upstream of the third control valve 13. The slurry tank 1, the cylinder 2 and the nozzle (work) 5 are connected with each other by pipes on which the control valves 11, 12 and 13 and the pressure sensors 14 and 15 are arranged.

The control section 20 comprises, for example, a sensor amplifier 21 which is input with pressure signals from the pressure sensor 14, 15 to amplify the pressure signals, a digital converter 22 for converting an analogue pressure signal into a digital pressure signal and a sequencer (a programmable controller) 23 which receives the pressure signals from the pressure sensors and comprises a control program. The control section 20 receives the pressure signals from the pressure sensors 14, 15 to process and calculate the values of the pressure signals and controls the fluid abrasive machining apparatus 100. The control section 20, however, may have known constructions, which includes a control circuit or includes a personal computer, etc., other than the construction described above.

Next, the operation of the fluid abrasive machining apparatus 100 according to this embodiment having the above-mentioned construction will be explained. In the present embodiment, the type “A” control in which a control is performed at the upstream side of the piping line is employed. In other words, while the pressure of the upstream side of the piping line (the measured pressure of a first pressure sensor 14) is maintained at a constant pressure, the fluid abrasive machining operation is terminated when the pressure of the downstream side of the piping line (the measured pressure of a second pressure sensor 15) reaches a predetermined pressure, and thereby the required flow rate performance of the product is realized.

At first, in the cylinder 2, the piston 6 is moved to a rod side of the cylinder 2 and then the cylinder 2 sucks the slurry 7 from the slurry tank 1. At this time, the first control valve 11 is opened and the second control valve 12 is closed. In a state in which the cylinder 2 is fully filled with the slurry 7, the first control valve 11 is closed and the second control valve 12 is opened. Then, the third control valve 13 is opened, the piston 6 is moved to a cylinder direction (head side) in the cylinder 2 and the slurry is pumped to the nozzle 5. At this time, the piston 6 is moved so that the pressure P1 of the first pressure sensor 14 is maintained at constant. As the characteristics of the slurry 7, the length of the piping line, etc. are previously known, the target flow rate of the slurry and the approximate value of the pressure at the first sensor 14 at the same time are previously noted. The pressure of the first sensor 14 and that of the second sensor 15 are always transmitted to, and are monitored by, the control section 20.

In the fluid abrasive machining, as the diameter of the nozzle 5 is initially small, the pressure loss at the nozzle 5 is large so that the flow rate of the slurry 7 is low and the pressure difference dp between the pressure P1 of the first sensor 14 and the pressure P2 of the second sensor 15 is small. When the machining operation proceeds, the diameter of the nozzle 5 is increased, the flow rate of the slurry 7 flowing through the nozzle increases and the pressure difference dp increases. As the pressure P1 is maintained at constant, the pressure P2 is monitored and is compared with the specific pressure value which is previously memorized in the control section 20. When the pressure P2 reaches a specific pressure value, that is, the pressure difference dp reaches a specific pressure difference value, the third control valve 13 is closed and the operation of the cylinder 2 is terminated. The pressure difference dp reaches the specific pressure difference value so that the flow rate of the fluid flowing through the nozzle 5 must reach the specific flow rate as explained above. Thus, the fluid abrasive machining of the nozzle 5, which is a work to be machined, is performed so that the nozzle 5 has a specific working performance. The fluid abrasive machining apparatus 100 may be formed so that the third control valve 13 is closed and the slurry 7 from the cylinder 2 is bypassed when the machining operation is stopped.

A second embodiment of the present invention will be now described below. The construction of the fluid abrasive machining apparatus of the second embodiment is basically the same as that of the first embodiment and has the construction shown in FIG. 1. The difference between the first embodiment and the second embodiment is only in a way of controlling the fluid abrasive machining operation. Therefore, the construction of the fluid abrasive machining apparatus of the second embodiment is not described here.

In the second embodiment, the type “B” control in which a control is performed at the downstream side of the piping line is employed. In other words, on the contrary of the first embodiment, in this type “B” control, the pressure P2 of the downstream side of the piping line is maintained at constant and at the time when the pressure P1 of the upstream side reaches a specific pressure value, the fluid abrasive machining operation is terminated and thereby, the required flow rate of the fluid flowing through the product (flow rate performance of the product) is realized.

The fluid abrasive machining method and the operation of the fluid abrasive machining apparatus 100 shown in FIG. 1 are basically the same as those of the first embodiment. The different points of the second embodiment from the first embodiment are in that the cylinder 2 is controlled so that the pressure P2 of the second pressure sensor 15 is maintained at a constant pressure and in that the pressure of the first pressure sensor 14 is monitored and when the pressure value of the first pressure sensor 14 reaches a previously memorized specific value, the third control valve 13 is closed and the operation of the cylinder 2 is terminated so that the operation of the fluid abrasive machining is terminated.

In the present embodiment, the cylinder 2 is controlled so that the pressure difference dp is increased, in other words, the pressure of the first pressure sensor 14 is increased, while the pressure P2 of the second sensor 15 is maintained at a constant pressure and, finally, if the pressure P1 has reached a specific pressure value, the pressure difference dp also reaches a specific pressure difference value. In this case, in accordance with a hargen poiseuille equation the flow rate of the slurry reaches a specific flow rate value.

Next, the effects and functions of the above-mentioned embodiments are explained.

The following effects can be expected from the fluid abrasive machining method and the fluid abrasive machining apparatus according to the first embodiment of the present invention.

In a process in which the flow rate of fluid flowing through a fine pore such as a fuel injection nozzle, etc. is adjusted by a fluid abrasive machining, a highly precise machining can be performed by monitoring pressure variations of a fluid flowing through the machined fine pore using a cheap pressure sensor, and without using an expensive flow meter, and by terminating the machining operation when the pressure reaches a specific pressure value and at the same time, the cost of the machining apparatus can be reduced. The above-mentioned pressure variations are caused as the result of the machining. When comparing a control method of a fluid abrasive machining using a flow meter, as the size of a pressure gauge is generally smaller than that of a flow meter and installation the pressure gauge is easy, the length of a piping line to a work therefrom can be reduced and the pressure gauge can be installed closer to the work and thereby it is possible to perform a highly precise machining.

In addition, as the present apparatus is not required to use a flow meter, it has endurance.

The fluid abrasive machining method or the fluid abrasive machining apparatus in the second embodiment of the present invention can be expected to provide the same effects as those in the fluid abrasive machining method or the fluid abrasive machining apparatus of the above-mentioned first embodiment.

In the above description or in the embodiments shown in the accompanied drawings, the supply device for supplying a slurry to the orifice which is a machined work is a cylinder which is a plunger type pump, however, the present invention is not limited to this and, for example, the supply device may be known types of pumps other than a plunger type pump or a known type of fluid supplying device. A slurry supply device, that is, a cylinder 2 is provided, however more than two of slurry supply devices may be provided.

Alternatively, in the above-mentioned embodiments, an example in which the present invention is applied to a machining of an orifice for a fuel injector of a diesel engine is shown, however the present invention is not limited to this and for example, the present invention may be applied to a machining of an orifice other than the above or to a machining of a precise fine pore, such as a tip of a fuel injection nozzle, an injection hole of a caburetor, an orifice for regulating fluid flow-rate, an injection nozzle for a printer, etc.

The above-mentioned embodiments are examples of the present invention and in no case is the present invention limited by the embodiments but it is specified only by the items described in claims and various embodiments other than those mentioned are possible.

While the invention has been described by reference to specific embodiments chosen for the purposes of illustration, it should be apparent that numerous modifications could be made thereto, by those skilled in the art, without departing from the basic concept and scope of the invention. 

1. A fluid abrasive machining method for abrasively machining a fine pore on a work to be machined by supplying a slurry, which is an abrasive machining fluid, from a supplying device to the work to be machined comprising steps of: supplying the slurry to the work to be machined from the supplying device; measuring a first pressure upstream in a discharge side of the supplying device; measuring a second pressure downstream of a measuring point of the first pressure and at an upstream side of the work to be machined; calculating a pressure difference between the first pressure and the second pressure; and terminating a machining operation when the pressure difference reaches a specific value.
 2. The fluid abrasive machining method as set forth in claim 1, wherein a control is performed so that the first pressure is always maintained at substantially constant during a fluid abrasive machining operation.
 3. The fluid abrasive machining method as set forth in claim 1, wherein a control is performed so that the second pressure is always maintained at substantially constant during a fluid abrasive machining operation.
 4. The fluid abrasive machining method as set forth in claim 1, wherein an object to be machined work is a fine pore of a fuel injector for a diesel engine.
 5. A fluid abrasive machining apparatus for abrasively machining a fine pore on a work to be machined by supplying a slurry, which is an abrasive machining fluid, to the work to be machined comprising: a supplying device for supplying the slurry; a measuring means for measuring a pressure difference between a first pressure at an upstream in a discharge side of the supplying device and a second pressure at a downstream of a measuring point of the first pressure and at an upstream side of the work to be machined; and a terminating means for terminating a machining operation when the pressure difference reaches a specific pressure difference value.
 6. The fluid abrasive machining apparatus as set forth in claim 5, further comprising: a first pressure sensor for measuring the first pressure; and a second pressure sensor for measuring the second pressure.
 7. The fluid abrasive machining apparatus as set forth in claim 5, wherein the work to be machined is a fuel injector for a diesel engine. 